Abstract: Mycobiota composition associated with DON-treated and not treated wheat haulms,buried in three different soils was evaluated. DON did not affect number and species profile offungal isolates occurring in wheat debris after 7d of incubation. F. oxysporum isolated fromhaulms were confirmed for their identity by TEF sequencing and submitted to molecular typingby AFLP, in order to assess the effect of DON and soil type on genetic variability. Based on bothanalyses, F. oxysporum grouped into four main clades, independently from the soil of origin andthe presence of DON in the baits. Isolates of Pythium spp., F. oxysporum (from the previousexperiment) and Trichoderma spp. (from our collection) were tested for their ability to grow inpresence of DON. Ten Trichoderma, 56 F. oxysporum and 2 Pythium isolates showed astatistically comparable growth rate in presence/absence of DON. Isolates not affected by DONwere tested against F. culmorum and F. graminearum mycotoxigenic isolates. Effects of Pythiumand Trichoderma against F. oxysporum were also evaluated. Pythium isolates showed a variablegrowth inhibition activity against F. culmorum, did not inhibit F. graminearum but parasitizemacroconidia of both. F. oxysporum did not inhibit pathogens and was not affected by the otherantagonists. Only three Trichoderma strains showed antagonistic and mycoparasitic activityagainst the pathogens and T. gamsii 6085, the best antagonist, was used in an in vitro competitiontest on natural substrates (wheat straw and rice), using qPCR to estimate the effect on pathogens’growth. Competition test on rice confirmed its ability to antagonize. On wheat straw, an extremeoligotrophic environment, T. gamsii 6085 seemed to develop very badly and did not affect thegrowth of both pathogens. This research aimed at selecting microfungi able to antagonize FHBagents and/or to compete with them for cultural debris in a multitrophic perspective.